Navigation aiding radio beacon system



June 2,1942. R. J. KEMP 2,284,873

NAVIGATION AIDING RADIO BEACON sYsTEM Filed April 19, 1940 2sheets-sheet 1 nnentor Holad cl.' Kem Cttorneg June 2,A 1942.

R. J. KEMP 2,284,873

NAVIGATION AIDING RADIO BEACON SYSTEM l Filed April 19, 1940 2sheets-sheet 2 LFI- *5f/,9F53

.Z0 Wal/f f Z IW-f -s/Mpf/e P/crz/e Beso. :E 75T E@ f Uf/a1 :'-J QPatented June 2, 1942 UNTED STATES PATE zagen orifice NAVGATIONAIDINGRDIO BEACON SYSTEM poration of Delaware Application April 19,1940, Serial No. 330,457 In Great Britain April 19, 1939 (Cl. Z50-11)Claims.

This invention relates to navigation aiding radio systems and moreparticularly to such systems of the television type, i. e. of the typewherein information as to the bearing of a transmitter with reference toa receiver is obtained by a cooperating receiver in the form of atelevision picture.

The object of the present invention is to provide improved navigationaiding radio beacon systems of the television type wherein the bearingdiscrimination shall be of a high order and wherein the liability todisturbance by interference shall be small. The invention is applicableboth to transmitters and receivers.

According to this invention as applied to transmitters a navigationaiding radio beacon transmitter installation of the television typecomprises means for radiating alternately and periodically tworadiations representable by similar but oppositely disposed intersectingpolar diagrams which together produce an equi-signal zone along the lineof intersection, the rate of alternation of said diagrams being abovethe rate of persistence of vision, means for rotating the alternateddiagrams about the transmitter, means for modulating the radiationcorresponding to each diagram with picture signals corresponding to ascanned picture indicative of the momentary direction of the equi-signalzone, means for also modulating said radiation with scanning line synchronizing impulses and means for also modulating said radiation witha framing synchronising signal for each alternate picture-modulateddiagram, i. e. so that a framing synchronising signal is included withthe signals sent out on one but not on the other, of the two diagrams.At a cooperating receiver the received television signals are translatedinto reproduced pictures in any convenient way known per se, and linesynchronisation is obtained by means such that the length of the sweepin the line direction is dependent upon the strength of the receivedline synchronising signals.

One way of carrying out this invention is illustrated in theaccompanying drawings in which Fig. 1 is a circuit diagramofvan'embodiment of this invention, Fig. 2 is a scanning disc, Fig. 3 isthe schematic diagram of a receiver and Fig. 4 illustrates receivedpictures corresponding to various bearings.

Referring to Fig. 1 there is provided at th transmitting installation anaerial systemconsisting of a frameaerial 2, and an omni-directionalaerial l5-an open aerial-which con-v jointly produce a cardioid polarradiation diagram in accordance with well known principle. An electricmotor l5, or the like, continuously rotates the frame aerial at apredetermined speed the connection being represented by the dotted line.(For convenience of representation, the frame aerial is shown separatedfrom the shaft on which it is mounted.)

Rotated synchronously with the frame aerial is a compass card l or otherdevice indicative of the momentary orientation of said frame aerial. Asmall portion of this compass card, or other device, is continuouslyscanned by means to be described hereinafter to produce picture signalswhich together with synchronising signals (obtained as will hereinafterbe described) are applied to any suitable modulated carrier wavetransmitter to produce a modulated carrier wave output. This output isfed to the two aerials and the relative sense of coupling of theseaerials with respect to the transmitter is periodically` reversed at arate above the persistence of vision. For example, the ends of the frameaerial (between which is connected a tuning condenser as in the ordinaryway) may be connected through blocking condensers I3, I4, to the anodeof two diodes 9, I0, one to each, the cathodes of said diodes beingconnected together and to one end of a carrier frequency circuit 8constituting the modulated carrier wave output circuit of thetransmitter proper. The open aerial is connected, for example, throughan adjustable resistance, to the same tuned circuit, e. g. to anintermediate tap thereon, and the diodes are made alternatelyconductive, 'whereby rst one sense of relative coupling will be obtainedand then the other. Accordingly with this arrangement the diodes aremade alternatively conducting, two similar but opposite intersectingcardioids being thus obtained, the line of intersection being of anequisignal line. The required alternate switching of the two diodes isobtained by means of an alternating potential applied thereto.

In the specific embodimentl now being dehaving two spiral half turnsbeing oppositely displaced with respect to a diameter of the disc andthe inner end of one half turn being on the same end of the diameter asthe outer end of the each two successive pictures.

and light from the selected (changing) portion of P the compass cardpasses through the scanning apertures a on one side of the centre ofthedisc to Y a photo-electric cell 3 whose output is, after suitableamplication in the amplier represented in block diagram at Il, employedyto modulate the carrier wave transmitter'. The modulator and localoscillator are represented in block diagram respectively at 5 and l.Light 'from' a`constant source is also passed through the synchronizingapertures b of the disc on the opposite side of the centre thereof to asecond photo-electric cell 23, Whose output is mixed at 4 with that fromthe cell already referred to.

The electric motor also drives or incorporates an alternatorll whoseoutput is applied to the primary of the transformer already mentioned,this alternator producing one sine wave per revolution of the scanningdisc. Accordingly, due to the alternate conductivity of the diodes, 180phase reversal of the frame aerial E. M. F. will be obtained at everyhalf cycle of the switching or generator frequency.

As will be seen, in every half revolution of the scanning disc thetelevision picture will be scanned and line synchronizing signals (dueto the line synchronizing slots b in the disc) will beobtained, thepicture signals and the line synchronizing signals being transmittedfrom the two aerials. Since, however, there is only one enlarged orframing synchronising slot there will only be one framing synchronizingsignal for As will be obvious the two successive pictures are sent oneby the radiation representable by one cardioid diagram and the other bythe radiation representable by the other.

A typical receiver is illustrated in Fig. 3. a'receiver has an ordinarycathode ray tube television receiver, and if the synchronizing signalsas received are selected by-suitablelters 24, 26, amplified, and appliedto non-oscillating sawtooth wave Shapers, or cathode ray deflectinggenerators 28, in such manner that the ampli- Such A amplitude.

due north of the transmitter would receive two equal images of thenumber 180, as illustrated in Fig. 4. At the same instant a receiverlocated at a point northeast of the transmitter would ree ceivetwonarrow pictures of unequal height. Since the vline synchronisingpulses driving the vertical saw tooth wave shaper or generator 30 at thereceiver, are contained in both cardioids, the relative heights of thepictures will have changed in proportion to the relative cardioid Alsobecause only one cardioid contains a framing pulse driving thehorizontal saw toothV wave Shaper or generator 28 the width of 'thepictures will have diminished in proportion tude of the synchronisingpulsesv directly determines the length of the line sweeps, when thereceiving station is on the equi-signal line the two television picturesalternately transmitted will be exactly similar to one another and willappear side by side on the screen of the cathode ray tube 32. However,when the receiver is not on the equi-signal line the two pictures willnot be of the same size nor of the same shape, for' one will be eithertaller or shorter than the other, depending upon the position of thereceiving station with reference to the equi-signal line. Accordinglythe bearing indicated by the received television pictures when saidpictures are alike as to-size and shape, will depend on the relativebearing of the transmitter and receiver. A wave shaper of the typerequired might include a condenser connected so as to be rapidly chargedby the synchronizing impulse applied through a rectiiier, and slowlydischarged bya resistor. The

- maximum voltage across the condenser for each cycle would therefore beproportional to the amplitude of the applied impulse, and asaw to theamplitude of that one cardioid. Still at the same instant, a receiverdue east of the transmitter would produce only a vertical line, asillustrated, because in this direction the eld modulated with horizontalscanning impulses is zero. At the same instant a receiver due south isagain on the equi-signal line and two equal orY balanced picturesappear. Thev southwest position is similar to the northeast except thathorizontal scanning now predominates and wide pictures are produced.Still at the same instant, a receiver west of the transmitter wouldreceive but a single picture since only the cardioidis received whichhasboth horizontal and vertical impulses. Y Considering now the natureof the picture at a given receiver at successive time intervals as theloop is rotated, it will be appreciated that the pictures on the screenwill continuously change. In the first place, their relative size andshape will change progressively through the Vstages pointed out above,since the result is the same whether one considers the reception atvarious points about a fixed loop, or the reception at a fixed point asthe loop is rotated.` In the second place, the numbers appearing onthescreen will also change from 0 to 360 as the loop-and the compass cardrotate. Thus when the receiver is due north of the transmitter, the. twofigures will be equal or balanced when a 0 appears and when a appears.-When thev receiver is northeast of the transmitter, the gures 4will beequal when the numbers 45V and 225 appear, and so forth. Y

It will be seen that an automatic indication of sense is given. One canadopt theconvention, for. example, that afbalancefollowing the singlepicture is the true bearing and .'a balance following the vertical lineis thereciprocal bearing. Theaccuracyto which the bearing can beVdetermined is ,enhanced by the factthat'the lines which areco-linear-at balance only.

The. transmitter above described is capableof `considerable modicationin detail withoutde parting from the invention; for example electronfeas-1,873

cameras or so-called iconoscopes may be used for picture transmission inplace of mechanical scanning systemssuch as that described, and

other information-e. g. identication symbols of the transmittingstation-may be included in the televised picture transmitted. Again,instead of two pictures being transmitted for each revolution of thedisc 20, matters may be so arranged that only one picture istransmitted, the resultant received picture lbeing divided into two, thetwo halves of the single4 picture bearing the same relationship to eachother .as do the two pictures inthe severalA diagrams of Figure 3. Thismodication involves, principally, the rearrangement of apertures a. intoone spiral Vinstead'of into two half-spirals. f

As previously stated the invention is applicable to directionalreceivers as well as to directional transmitters and may be applied toprovide `a direction nding receiver of the television type adapted tocooperate with an omni-directional radio beacon modiiied by the additionof a picture modulation for the purpose of identication. Such a receiverwould be, in effect, the analogue of the transmitter hereinbeforedescribed. In one such construction the receiver, like the transmitterabove described, obtains its directional eect by employing the sameprinciple of periodically alternating between two diagrams whichintersect to denne an equi-signal zone, e. g. it may incorporate aerialsand an associated diode switching circuit whereby similar but oppositeintersecting cardioids are alternately obtained. Again, as in thetransmitter case, bearing indication is given by comparing and balancingtwo side-by-side patterns produced on the screen of a cathode ray tube.These patterns are formed by saw-tooth wave generators of thenon-oscillating type controlled by the amplitudes of the synchronisingpulses as received from the cooperating transmitter. The control grid ofthe cathode ray tube is operated by the picture signals. The lowfrequency saw-tooth generator is made to sweep at half the transmittedfrequency, e. g. for a transmitted frame frequency of 20 R. P. S. a scanfrequency of R. P. S. would be used. The oscillator providing theswitching frequency also provides the scan frequency and is preferably amultivibrator which can be readily controlled at its natural frequencyof 10 R. P. S. (for example) by a synchronising signal of R. P. S.Alternatively, of course, one frame synchronising signal could betransmitted for every two pictures.

I claim as my invention:

1. A navigation aiding radio beacon transmitter installation of thetelevision type comprising means for radiating alternately andperiodically two radiations representable by similar but oppositelydisposed intersecting polar diagrams which together produce anequi-signal zone along the line of intersection, the rate of alternationof said diagrams being above the rate of persistence of vision, meansfor rotating the alternated diagrams about the transmitter, picturemodulating means for modulating the radiations corresponding to bothdiagrams with picture signals corresponding to a scanned pictureindicative of the momentary direction of the equi-signal zone, means foralso modulating said radiations with scanning line synchronisingimpulses and means for also modulating the radiation corresponding toone of said diagrams with a framing synchronising signal so that aframing synchronising signal is included with the signals sent'out' onone but not on the other of the two diagrams.

2. A transmitter installation as claimed .in claim 1 wherein said meansfor radiating oppositely disposed intersecting polar diagramsA comprisesa frame aerial and an omni-directional aerial for producing cardioidpolar diagrams modulated with picture signals corresponding to acomplete picture indicative of said momentary direction.

3. A transmitting installation as claimed in claim 1 wherein saidpicture modulating means includes a scanning disc having two spiralhalfturns of scanning apertures the spiral half turns being oppositelydisplaced with respect to a diameter of the disc and the inner end ofone half turn being on the same end ofthe diameter asthe outer end ofthe other, a ring of line synchronising apertures or slots one for eachaperture in the spiral half turns, and, in the same ring with thesynchronising slots, a single elongated or enlarged frame synchronisingaperture positioned adjacent one end of the diameter which divides thespiral half turns.

4. A transmitting installation as claimed in claim 1 wherein saidpicture modulating means includes a scanning disc having two spiral halfturns of scanning apertures, the spiral half turns being oppositelydisplaced With respect to a diameter of the disc and the inner end ofone halfturn being on the same end of the diameter as the outer end ofthe other, a ring of line synchronising apertures or slots one for eachaperture in the spiral, and, in the same ring with the synchronisingslots, a single elongated or enlarged frame synchronising aperturepositioned adjacent said diameter.

5. A navigation aiding radio beacon transmitter installation of thetelevision type comprising means for radiating alternately andperiodically two radiations representable by similar but oppositelydisposed intersecting polar diagrams which together produce anequi-signal Zone along the line of intersection, the rate of alternationof said diagrams being above the rate of persistence of vision, meansfor rotating the alternated diagrams about the transmitter, picturemodulating means for modulating the radiations corresponding to bothdiagrams with picture signals corresponding to one half of a pictureindicative of the momentary direction of the equi-signal zone, means foralso modulating said radiations with scanning line synchronisingimpulses and means for also modulating the radiation corresponding toone of said diagrams with a framing synchronising signal so that aframing synchonising signal is included with the signals sent out on onebut not on the other of the two diagrams.

6. A transmitter installation as claimed in claim 1 wherein said picturemodulating means includes a compass card rotatable with said frameaerial, and means for scanning a portion of said compass card to producemodulating signals so that the line of intersection of said oppositelydisposed diagrams rotates continuously and synchronously with saidcompass card.

7. A navigation aiding radio system comprising in combination means forradiating alternately diirerent directional radiations modulated byvisual bearing indications and by synchonizing impulses, means forreceiving said radiations, means for separately reconstituting picturescorresponding to and bearing indications from said two radiations, saidvisual means for varying the relative size of said picturescorresponding to said different directional Vradiations 'in' accordancewith the intensity of said diieren't directional radiations,respectively.

8. A device of the character described in claim 7 in which said meansfor reconstituting pictures corresponding to said visual bearingindications includes a cathode ray tube having ray deflecting means,means for deriving separate line and frame synchronizing impulses fromsaid signal,

and means for applying said derived synchronizing impulses to saiddeecting means.

9. A device of the character described in claim 7 in which said means.forreconstituting pictures corresponding to said visual lbearingindication includes a cathode ray tube having ray deflecting means,means for deriving separate line and frame synchronizing impulses fromsaid signal, means for producing saw tooth line drawing and framingvoltages corresponding in amplitude to the amplitude of said line andframe synchronizi ing impulses, respectively, and means for applyingsaid'voltages 'to said deflecting means.

10. A navigation aiding radio system of the type wherein informationinthe form of a television picture is obtained of the bearing of atransmitter with respect to a receiver comprising in combination meansfor radiating a rotating beacon signal representable by oppositelydisposed intersecting polar diagrams which together produce anequi-signal zone along the line of intersection, means for modulatingsaid signal with television pictures indicative of the momentarydirection of said beacon, means for receiving said signal,meansgresponsive to said modulations for producing two visual picturesthe dimensions of which at any instant are determined by the amplitudesof said intersecting polar diagrams, whereby Ibalanced pictures areproduced by a receiver located on said equi-signal zone.

ROLAND VJOHN KEMP.

